How Not to Write a Screenplay: 101 Common Mistakes Most Screenwriters Make is an interesting book and a pretty quick read. It's very entertainingly written, and makes a lot of sense. Unlike William Goldman's books (Adventures in the Screen Trade and Which Lie Did I tell?), I don't think that it would be interesting except for those with an interest in screenwriting.
For those, like me, who have an interest in screenwriting but are just starting, I heartily recommend it.
Incidentally, one of the things it mentions but doesn't really harp on is how much of a group endeavor a movie is. In the section where he recommends against including camera directions, aside from them being distracting, he points out that the director and cinematographer are going to ignore them anyway. Goldman mentioned that too.
Essentially, once a screenplay gets accepted and people start signing on, they're all going to want to have creative influence on the story, and so far it seems to be recommended to make sure to give leeway for that in places where it doesn't matter so that people are less likely to screw around with the parts that do matter. There's probably something to that, of course, but I wonder if it might not be better to try to avoid getting so emotionally attached to someone as one's own that won't be one's own. Of course you have to at least like a story to write it, and it probably really helps to love it, but that also seems counter-productive to one's health. I imagine that it's kind of like children. If you don't approach them with a pretty healthy dose of realizing that they're not going to turn out like you expect, you're not likely to be a good parent and you're just going to suffer.